Single-nanoparticle-resolution in situ measurements provide time-dependent snapshots of the dynamic individual nanoparticles, and thus the heterogeneous interactions between nanoparticles can be elucidated and distinguished from the ensemble. This approach reveals direct and detailed information on colloidal nanocrystal growth and assembly mechanism and reaction kinetics. However, conventional high-resolution imaging methods including electron microscopy typically provide the static information of structures without in situ information and require complicated setup and procedures under harsh conditions (e.g., vacuum). For these reasons, fluorophore-based single-molecule-level optical imaging and analysis methods are mainly used in obtaining the dynamic information on intermolecular interactions, but suffer from the blinking and bleaching problems of fluorophores. Further, discerning short-range molecular interactions of multiple components with fluorophore labels is highly challenging, and even with fluorescence resonance energy transfer, the measurable distance is limited to 10 nm and interpretation becomes difficult for multi-component systems. These are serious issues for real-time studies of the interactions between molecules and nanoparticles and obtaining reproducible and reliable quantitative data for many analyses. Another important issue of these conventional high-resolution optical methods is that dynamically moving objects cannot be individually and reliably analyzed and studied in a solution state because of their uncontrollable three-dimensional movements and the inability of optics to track all of the objects of interest. It should also be noted that, when these objects are fixed on a surface for high-resolution optical analysis, the dynamic behaviors of these objects cannot be studied. For all of these reasons, it would be extremely beneficial to develop a method that allows for in situ imaging and analysis of the interactions between freely moving nanoparticles with single-particle sensitivity. To obtain more reliable information and derive new principles from studying interacting particles, one must also track interactions from multiple reaction sites simultaneously with single-particle-level quantification data.